<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  .aaa{
    width: 200px;
    height: 100px;
    display: flex;
    flex-direction: row;
    /* flex-direction: column; */
    /* justify-content: center; */
    background-color: red;
    align-items: center;
  }

  .bbb{
    width: 50px;
    height: 50px;
    background-color: #bfa;
  }
</style>
<body>
    <div class="aaa">
      <div class="bbb">11</div>
    </div>
</body>
</html>